p150c1:1 Chapter 1: Describing Motion Units: how quantities in the physical world are described Basic Units: A set of units which can be used to express all physical quantities. Système International (S.I. = metric system)

p150c1:2 Common prefixes

p150c1:3 Converting units treat units as algebraic quantities Multiplying or dividing a quantity by 1 does not affect its value

p150c1:4 Speed displacement time tt xx

p150c1:5 Constant Speed average speed = instantaneous speed (at all times) displacement time Example 1.3: A woman standing in front of a cliff claps her hands, and 2.50 s later she hears an echo. How far away is the cliff? (speed of sound in air = 343 m/s) Example 1.4: If the speed limit is raised from 55 mph to 65 mph, how much time is saved on a 100 mile trip?

p150c1:6 Velocity: the true measure of motion = how fast, in what direction = speed (how fast) + direction(velocity is a vector) Vector: a quantity which has magnitude (how big) and direction => the magnitude of velocity is speed Displacement = change in position velocity is the rate of change of displacement average velocity vs. instantaneous velocity

p150c1:7 Acceleration: changes in motion = how fast,and in what direction velocity is changing acceleration is a vector for motion in one dimension: speed changes with time increasing/decreasing speed changes in direction of velocity usually assumed constant

p150c1:8 Velocity and Acceleration final velocity = initial velocity + change in velocity v v0v0 t at vfvf v v0v0 t vfvf v v0v0 t vfvf v v0v0 t vfvf

p150c1:9 Example 1.7: A car has an initial velocity of 20 m/s and and acceleration of -1.0 m/s 2. Find its velocity after 10s and after 50 s.

p150c1:10 Displacement, Time and Acceleration Example 1.8: A car has an initial velocity of 20 m/s and and acceleration of -1.0 m/s 2. Find its displacement after 10s and after 50 s.

p150c1:11 Displacement, Velocity and Acceleration Example 1.9: A car has an initial velocity of 20 m/s and and acceleration of -1.0 m/s 2. How far will it go before (momentarily) coming to rest?

p150c1:12 Problem Solving Tips Draw a diagram Write down all known quantities, identify on diagram. Write down all unknown quantities, identify on diagram. Find basic equation which relates each unknown quantity to known quantities. Solve equation for the desired unknown. “plug and chug”

p150c1:13 Acceleration of Gravity Historical Perspective: Attempts to describe motion (Aristotle, Galileo,...) Experiment and observation as the foundation of science idealizations and simplifications: ignoring air resistance g = 9.81 m/s 2 (9.78 at equator, 9.83 at poles) = 32 ft/s 2 a = g, acceleration is directed downwards

p150c1:14 Example 1.12 (variation) A penny is dropped from a building 300m high. How long does it take the penny to reach the ground? What is its velocity when it reaches the ground? Example 1.13 A stone is thrown upward with an initial speed of 16 m/s. What will its maximum height be? When will it return to the ground? Where will it be in.8 s? In 2.4 s?